Aims Under the background of changing carbon cycle process in forest ecosystems caused by global environmental change, the microbial carbon use efficiency（CUE） in forest rhizosphere soil is critical to determine the strength of microbial anabolism and catabolism in forest ecosystems. However, the variation and influencing factors of microbial CUE in rhizosphere soils at different altitudes remain undetermined.Methods Rhizosphere soil at six different altitudes spanning four forest belts in Taibai Mountain was sampled to determine the physical and chemical properties, extracellular enzyme activity, and characteristics of microbial community and vegetation. Based on the stoichiometric ratio, the soil microbial CUE was estimated. Furthermore,the variation in microbial CUE of rhizosphere soil along the altitude gradient was analyzed to quantify the influencing factors of microbial CUE.Important findings The results showed that the microbial CUE of rhizosphere soil exhibited an overall upward trend with the increase in altitude. The microbial CUE increased by 4.36% from 0.505 at the lowest altitude to 0.527 at the highest altitude, but decreased at 1 603 and 2 405 m. Based on the Mantel analysis, we identified four categories of factors（i.e., altitude, soil matrix, vegetation and microbe） that related to microbial CUE in rhizosphere soil. The variations of microbial CUE in rhizosphere soil are affected by multiple environmental factors, with the dominant factor being soil matrix（such as dissolved organic carbon（DOC） content, ammonium nitrogen（NH 4 + -N） content）, followed by vegetation. Furthermore, the altitude factor and the microbial factor explained 2.6% and 3.1% of the CUE change, respectively. Although the microbial factors exerted no significant impact on microbial CUE, soil matrix, vegetation and microbe jointly explained 47.0% of the microbial CUE change. The variance partitioning analysis（VPA） quantitatively revealed the contribution of environmental factors to the change of microbial CUE, where soil matrix and vegetation explained 17.0% and 5.7% of the variation, respectively. While the interaction between soil matrix and vegetation accounted for 31.9% of the changes in microbial CUE. The above results indicated that the high-altitude rhizosphere soil in Taibai Mountain has a high carbon sequestration potential, and the carbon sequestration of forest rhizosphere soil may decrease with the intensification of global warming. The vertical temperature difference and the vertical differentiation of the vegetation belt induced by altitude gradient will alter the growth and metabolism environment of microorganisms in the rhizosphere soil. The comprehensive effect of multiple environmental factors dominated by soil matrix impacts the CUE of soil microorganisms, and ultimately changes the assimilation and catabolism processes of soil carbon. The results of this study can provide a scientific basis for the carbon assimilation capacity and carbon sequestration potential of forest soil microorganisms in Qinling Mountains, as well as the forest soil carbon cycle under the background of global change.

[目的]研究秦岭太白山锐齿栎林4种不同海拔土壤微生物多样性及群落组成特征,以期阐明同一植被类型土壤微生物群不同海拔的变化规律及驱动因素.[方法]在秦岭太白山4个海拔梯度(1361.6、1524.2、1630.5和1769.3 m),选取排水较好、坡度较缓、长势适中的3个锐齿栎林标准样地(20 m×20 m),于2016年8月,用"S"型方法于每块样地进行0～10 cm土层的混合取样,利用高通量测序技术测定土壤微生物群落多样性及组成.[结果]1)不同海拔梯度的锐齿栎林土壤细菌多样性(α多样性和 β多样性)变化显著,但真菌多样性无显著变化.2)在细菌群落组成中,随海拔升高,放线菌的相对丰度显著降低,而变形菌和疣微菌的相对丰度显著增加,绿弯菌、芽单胞菌和硝化螺旋菌的相对丰度呈先增后降的变化;其他细菌类群如酸杆菌和浮霉菌的相对丰度呈不显著降低.在真菌群落组成中,作为2个优势菌门的担子菌和子囊菌的相对丰度随海拔增加的变化不显著.3)细菌多样性与土壤有机碳(SOC)含量、全氮(TN)含量、C:P和N:P显著正相关,其群落组成对海拔梯度的响应差异主要取决于土壤密度、温度、SOC、C:P和TN;真菌群落多样性及组成受土壤养分差异的影响较小.在植被相同但海拔不同的条件下,受气候及土壤养分的差异影响,细菌群落特征较真菌群落的变化明显.[结论]秦岭太白山锐齿栎林土壤细菌和真菌多样性沿海拔梯度呈先增后减的变化趋势.海拔对细菌群落的影响大于真菌群落.研究结果揭示了秦岭暖温带森林生态系统土壤微生物群落结构和组成的变化特征及影响因素,从而为深入理解森林生态系统土壤有机碳分解的微生物机制提供科学依据.